The purpose of the study is to identify objectively the behavioral patterns associated with organic characteristics found through intensive medical work-ups of children referred for hyperactivity. Both parents of a referred child independently complete a behavior checklist from which a standardized behavior profile is derived. Degree of inter-parent agreement is computed and the profiles are analyzed in order to classify children according to types of behavior patterns. Classification of children in this way is then compared with ratings of ward behavior, with the outcomes of the medical work-up, and with the effects of stimulant drugs to determine whether the behavioral typology corresponds to characteristics of the children identified clinically.